Hi there Bruce. This one gets asked a lot. The answer is that your play of FIBS is a perfectly valid play that can be made in a single move.

As long as the letters you play in a move form a valid word in a single row or a single column (in your case FIBS), it doesn't matter how many other words you form in the opposite direction by letters that happen to be there already.

Just to be sure I've interpreted you correctly, I've included a picture above of the situation I believe you are describing. In that picture, FIBS is a perfectly valid single play, that just happens to form TWEAKS (and hence, extra points!) in the process.

I hope that answers your question. Please feel free to continue the discussion using the comments link below if you like.